An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The → tangent of the complement of an arc or angle; abbreviation cot. If θ is an → acute angle of a → right angle, cot θ = (adjacent side)/(opposite side).

→ co-; → tangent.

1) A straight line or plane that touches a curve or curved surface at one and only one point. Conversely, a curve or curved surface that touches a straight line, curve, or curved surface at one and only one point.
2) In trigonometry, the function of an acute angle of a right triangle defined as the ratio of the length of the opposite side to that of the adjacent side.

From L. tangentem (nominative tangens), pr.p. of tangere "to touch," from PIE base *tag- "to touch, to handle" (cf. L. tactus "touch," Gk. tetagon "having seized," O.E. þaccian "stroke, strike gently"); tânžânt, loan from Fr.

1) Sâyân, pr.p. of sâyidan "to touch, to rub," variants sâbidan, pasâvidan; Khotanese sauy- "to rub;" Sogdian ps'w- "to touch;" ultimately Proto-Iranian *sau- "to rub."
2) Tânžânt, loan from Fr.

Pertaining to or of the nature of a tangent.

→ tangent + -ial variant of → -al.

That component of a an object's motion which is perpendicular to the observer's → line of sight.

→ tangential; → motion.

1) The instantaneous linear velocity of a body moving in a circular path. It is equal to the → angular velocity multiplied by the radius: v_t = ωr.
3) The component of the velocity of an object, such as a star, that is at right-angles to the observer's → line of sight; also known as transverse velocity. See also → radial velocity.

→ tangential; → velocity.

The → linearly polarized light that vibrates perpendicularly to an imaginary line joining the source to the point of observation.

Tangentially, adverb of → tangential; → polarized; → light.